This will make all instances share the same array for .contentRegistry, and if an instance tries to mutate it, it will affect other instances. Let's put the default registry on the prototype as ContentViewFactory.prototype.contentRegistry. And then in the constructor:

    this.contentRegistry = this.contentRegistry.slice(0);

This will basically copy the array for that instance. And then subclasses can just set their own contentRegistry on their prototype to change the behavior.